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Date:   Fri, 18 Oct 2019 07:48:05 -0700
From:   Jerry Snitselaar <jsnitsel@redhat.com>
To:     Joerg Roedel <jroedel@suse.de>
Cc:     Qian Cai <cai@lca.pw>, don.brace@microsemi.com,
        martin.petersen@oracle.com, linux-scsi@vger.kernel.org,
        jejb@linux.ibm.com, esc.storagedev@microsemi.com,
        linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org
Subject: Re: [PATCH] iommu/amd: Check PM_LEVEL_SIZE() condition in locked
 section
Message-ID: <20191018144805.ici3ewsvonlgketl@cantor>
Reply-To: Jerry Snitselaar <jsnitsel@redhat.com>
Mail-Followup-To: Joerg Roedel <jroedel@suse.de>, Qian Cai <cai@lca.pw>,
        don.brace@microsemi.com, martin.petersen@oracle.com,
        linux-scsi@vger.kernel.org, jejb@linux.ibm.com,
        esc.storagedev@microsemi.com, linux-kernel@vger.kernel.org,
        iommu@lists.linux-foundation.org
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On Fri Oct 18 19, Joerg Roedel wrote:
>On Thu, Oct 17, 2019 at 07:36:51AM -0400, Qian Cai wrote:
>>
>>
>> > On Oct 16, 2019, at 6:59 PM, Jerry Snitselaar <jsnitsel@redhat.com> wr=
ote:
>> >
>> > I guess the mode level 6 check is really for other potential callers
>> > increase_address_space, none exist at the moment, and the condition
>> > of the while loop in alloc_pte should fail if the mode level is 6.
>>
>> Because there is no locking around iommu_map_page(), if there are
>> several concurrent callers of it for the same domain, could it be that
>> it silently corrupt data due to invalid access?
>
>No, that can't happen because increase_address_space locks the domain
>before actually doing anything. So the address space can't grow above
>domain->mode =3D=3D 6. But what can happen is that the WARN_ON_ONCE trigge=
rs
>in there and that the address space is increased multiple times when
>only one increase would be sufficient.
>
>To fix this we just need to check the PM_LEVEL_SIZE() condition again
>when we hold the lock:
>
>From e930e792a998e89dfd4feef15fbbf289c45124dc Mon Sep 17 00:00:00 2001
>From: Joerg Roedel <jroedel@suse.de>
>Date: Fri, 18 Oct 2019 11:34:22 +0200
>Subject: [PATCH] iommu/amd: Check PM_LEVEL_SIZE() condition in locked sect=
ion
>
>The increase_address_space() function has to check the PM_LEVEL_SIZE()
>condition again under the domain->lock to avoid a false trigger of the
>WARN_ON_ONCE() and to avoid that the address space is increase more
>often than necessary.
>
>Reported-by: Qian Cai <cai@lca.pw>
>Fixes: 754265bcab78 ("iommu/amd: Fix race in increase_address_space()")
>Signed-off-by: Joerg Roedel <jroedel@suse.de>
>---
> drivers/iommu/amd_iommu.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
>diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
>index 2369b8af81f3..a0639e511ffe 100644
>--- a/drivers/iommu/amd_iommu.c
>+++ b/drivers/iommu/amd_iommu.c
>@@ -1463,6 +1463,7 @@ static void free_pagetable(struct protection_domain =
*domain)
>  * to 64 bits.
>  */
> static bool increase_address_space(struct protection_domain *domain,
>+=09=09=09=09   unsigned long address,
> =09=09=09=09   gfp_t gfp)
> {
> =09unsigned long flags;
>@@ -1471,8 +1472,8 @@ static bool increase_address_space(struct protection=
_domain *domain,
>
> =09spin_lock_irqsave(&domain->lock, flags);
>
>-=09if (WARN_ON_ONCE(domain->mode =3D=3D PAGE_MODE_6_LEVEL))
>-=09=09/* address space already 64 bit large */
>+=09if (address <=3D PM_LEVEL_SIZE(domain->mode) ||
>+=09    WARN_ON_ONCE(domain->mode =3D=3D PAGE_MODE_6_LEVEL))
> =09=09goto out;
>
> =09pte =3D (void *)get_zeroed_page(gfp);
>@@ -1505,7 +1506,7 @@ static u64 *alloc_pte(struct protection_domain *doma=
in,
> =09BUG_ON(!is_power_of_2(page_size));
>
> =09while (address > PM_LEVEL_SIZE(domain->mode))
>-=09=09*updated =3D increase_address_space(domain, gfp) || *updated;
>+=09=09*updated =3D increase_address_space(domain, address, gfp) || *updat=
ed;
>
> =09level   =3D domain->mode - 1;
> =09pte     =3D &domain->pt_root[PM_LEVEL_INDEX(level, address)];
>--=20
>2.16.4
>

Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>